Hello!

I'm unable to launch the game via the StardewModdingAPI.exe.

The black window pops up, and it populates the following text:

Created log instance
System.MissingMethodException: Method not found: 'System.Threading.Tasks.Task System.Threading.Tasks.Task.Run(System.Action)'.
at StardewModingAPI.Log.AsyncColour(Object message, ConsoleColor olour)
at STardewModding.API.Log.AsyncY(Object message)
at StardewModdingAPI.Program.Main(straing[]args)

But nothing else happens. Any keyboard interaction with the program crashes it.
I have uninstalled and reinstalled it several times, following every youtube tutorial (IDED included) to no success.

Please help, I'm going insane :(

Great news, future people with my problem! I've solved it.

I thought Steam required a updated .NET Framework, so I never even considered it was outdated.
It was!
A quick install and reboot, and SMAPI successfully launches my game.

Happy farming, all!

Glad you were able to solve it! :)